A dielectric porcelain composition tends to exhibit an increased dielectric loss as the frequency used becomes high. Therefore, a dielectric porcelain composition which exhibits a high relative dielectric constant (hereinafter referred to as ".epsilon..sub.r ") and a high unloaded Q value (hereinafter referred to as "Qu") in the microwave frequency range has been desired. As this kind of a dielectric porcelain composition there has heretofore been known one having a crystalline structure comprising two phases, i.e., perovskite phase and illmenite phase (as disclosed in JP-A-2-129065 (The term "JP-A" as used herein means an "unexamined published Japanese patent application")). A dielectric porcelain composition comprising MgTiO.sub.3 and TiO.sub.2 mixed with a predetermined amount of CaTiO.sub.3 has been known as well (as disclosed in JP-A-52-118599).
However, the former dielectric porcelain composition is disadvantageous in that it contains a considerable amount of other components such as Nd.sub.2 O.sub.3, La.sub.2 O.sub.3, PbO and ZnO and doesn't always have a high Qu. The latter dielectric porcelain composition comprises TiO.sub.2 as an essential component and thus is disadvantageous in that the temperature coefficient of resonant frequency (hereinafter referred to as ".tau..sub.f ") makes a great positive or negative change when the mixing ratio of CaTiO.sub.3 falls within a range of from 3 to 10% by weight, making it difficult to adjust the temperature coefficient .tau..sub.f to a small value close to zero.